1. Field of the Invention
The present invention relates to a wiring board, a semiconductor device, and a process for the production of wiring boards, and particularly to an effective technology applied to a semiconductor device of LGA (Land Grid Array) type.
2. Prior Art
Heretofore, there has been a semiconductor device of CSP (Chip Scale Package) type wherein a ball-like bump (ball terminal) is connected as an external connection terminal for connecting the semiconductor device to a mount board such as a mother board, or an external device as the one wherein a semiconductor chip has been mounted on a wiring board.
The above-described semiconductor device of CSP type is arranged as shown in, for example, FIGS. 1A and 1B, in such that a wiring board in which an electric wiring 2 and an external connection terminal 2A are disposed on a first principal plane (a side of the front) of an insulating substrate 1 such as a polyimide tape is placed, and a semiconductor chip 6 is mounted on the surface on which the electric wiring 2 of the wiring board (the insulating substrate 1) has been formed in, for example, such a manner that its external electrode 601 is opposed to the above-described surface wherein the electric wiring 2 of the above-described wiring board is connected with the external electrode 601 through a protrusion conductor 13. FIG. 1B is a sectional view taken along the line C-Cxe2x80x2 of FIG. 1A. Furthermore, a gap between the wiring board (insulating substrate 1) and the semiconductor chip 6 is subjected to under-filling sealing by means of a sealing insulator 9 made of, for example, an epoxy-based thermosetting resin and the like in the above-described semiconductor device. Besides, an opening 101 for connecting a ball terminal is defined at a predetermined position of the insulating substrate 1, for example, a site where, for example, the external connecting terminal 2 has been disposed, and it is guided to a second principal plane opposed to the first principal plane by means of a through hole plating 15 provided around the opening 101 or a conductive member filled inside the opening 101. To the opening 101, a ball terminal 16 made of, for example, a Pbxe2x80x94Sn based solder and the like is connected.
In case of the above-described semiconductor device of CSP type, however, when the ball terminal 16 of the semiconductor device of CSP type is connected with an electric wiring 11 of a mount board 10 such as a mother board to mount the semiconductor as shown in FIG. 2, a height t extending from a mounting surface 10A of the above-described mount board 10 to the upper surface 6A of the semiconductor chip 6 in the semiconductor device becomes higher by an amount corresponding to a height txe2x80x2 of the above-described ball terminal 16. For this reason, a container (casing) for containing the mount board 10 on which the above-described semiconductor device of CSP type has been mounted becomes thicker, so that it is difficult to reduce a size of the semiconductor device.
Moreover, since the external electrode 601 of the above-described semiconductor chip 6 is connected with the electric wiring 2 by means of the protrusion conductor 13 in the case when the semiconductor chip 6 is subjected to flip-chip junction on the wiring board, a distance (stand-off) extending from the insulating substrate 1 to a circuit-forming surface of the semiconductor chip 6 becomes higher, so that the semiconductor device becomes thicker, whereby it is difficult to thicken the same.
In this connection, there is a semiconductor of LGA type wherein an unrelieved external connecting terminal is disposed in place of the above-described ball terminal 16 as a manner for preventing from an appearance of a thicker semiconductor device. In the above-described semiconduct or device of LGA type, an electric wiring 2 is formed on a principal plane of an insulating substrate 1, and an external connecting terminal (land) 17 is formed on a surface opposed to the surface on which the electric wiring of the above-described insulating substrate 1 has been formed as shown in FIG. 3. In this case, the electric wiring 2 is electrically connected with the land 17 by means of a through-hole plating 15 provided around a via hole 102 defined on the above-described insulating substrate 1. The outer periphery of the land 17 may be covered with a protective film such as a solder resist. In case of the above-described semiconductor device of LGA type, a plating layer 4B prepared by laminating a nickel plating layer and a gold plating layer having good solderability on a surface of the land 17. In this respect, a soldering paste or the like has been previously applied onto a predetermined position of the surface of the above-described land 17 or the electric wiring 11 on a mount board 10, and then, the semiconductor device is mounted.
In case of such a semiconductor device of LGA type, since there is no ball terminal 16 as in a semiconductor device of CSP type, a height of the semiconductor device can be reduced in the case when it is mounted on the mount board 10, whereby the present semiconductor device can be made thinner than that of the above-described semiconductor device of CSP type.
A wiring board used in the above-described semiconductor device of LGA type is prepared as described here in after. First, conductive thin films 18 made of a copper foil and the like are formed on both principal planes of an insulating substrate made of a polyimide tape and the like, the conductive thin film on a side of either principal plane is etched to form an external connection terminal 17, and then, a via hole 102 is defined at a predetermined position of the above-described external connection terminal 17 by means of laser or the like as shown in FIG. 4A.
Thereafter, a through-hole plating 15 is formed around the via hole 102 as shown in FIG. 4B, and an electric wiring 2 is formed from the conductive thin film 18 on the surface opposed to that on which the above-described external connection terminal 17 has been formed by the use of, for example, an additive plating method or the like method. In this occasion, a connection terminal 2A, which is to be connected to a through-hole plating 15 in the above described via hole 102, is formed on the electric wiring 2.
Then, as shown in FIG. 4C, a plating layer 4A prepared by laminating, for example, a nickel plating layer and a gold plating layer is formed on a surface of the above-described electric wiring 2 as well as a plating layer 4B prepared by laminating, for example, a nickel plating layer and a gold plating layer is formed on a surface of the above-described external connection terminal 17. A wiring board used for a semiconductor device of LGA type is obtained in accordance with the procedure as described above.
For instance, a semiconductor chip 6 is subjected to flip-chip mounting on a surface on which the electric wiring 2 of a wiring board prepared in accordance with the above-described procedure has been formed, and a liquid resin is poured in between the above-described wiring board (insulating substrate 1) and the semiconductor chip 6 to complete under-filling sealing, whereby a semiconductor device of LGA type can be obtained as shown in FIG. 3.
In a semiconductor device of CSP type shown in FIG. 1, however, it is required to maintain certain spacing in between the openings 101 so as not to be in contact with the ball terminals 16 each other. The same situation is observed in also the semiconductor device of LGA type shown in FIG. 3 wherein it is required to maintain a certain spacing in between the via holes 102 so as not to be in contact with the external connection terminals (lands) 17 each other. In this respect, via holes 102 must be formed with a certain spacing from a constructional point of view in case of any of the semiconductor devices described above, otherwise it results in a drawback for downsizing of its package.
Furthermore, in a conventional semiconductor device of LGA type described above, the electric wiring 2 is formed on a principal plane of the insulating substrate 1, and the external connection terminal (land) 17 is formed on the surface opposed to that on which the electric wiring has been formed in case of preparing a wiring board for mounting a semiconductor chip. In this constitution, a tape material wherein a conductive thin film such as a copper foil has been disposed on the opposite surfaces of the insulating substrate 1 is employed. For this reason, there has been such a problem that its material cost increases, besides its manufacturing steps increase, so that the resulting manufactures"" costs for wiring board and semiconductor device increase.
Accordingly, an object of the present invention is to provide a technology by which a semiconductor device wherein a semiconductor chip has been mounted on its wiring board can be thinned.
Another object of the present invention is to provide a technology by which a height extending from a mount board to the top surface of its semiconductor device can be reduced in the case when the semiconductor device wherein a semiconductor chip has been mounted on its wiring board is mounted on the mount board.
A further object of the present invention is to provide a technology by which manufacturing steps for a wiring board used in a semiconductor device of LGA type can be simplified, and its cost of manufacture can be reduced.
The above described and other objects as well as novel features of the present invention will become apparent from the description and the appended drawings of the specification.
(1) In order to achieve the above-described objects, a wiring board according to the present invention wherein an opening is defined at a predetermined position of a film-like insulating substrate, an electric wiring provided with a connection terminal covering the opening is disposed on a principal plane of the insulating substrate, and a conductive member to be connected with the connection terminal of the electric wiring is disposed inside the opening, which comprises the conductive member having a thickness from a surface on which the electric wiring of the insulating substrate has been disposed being thinner than that of the insulating substrate.
According to the above-described wiring board, since the opening is defined on the insulating substrate and the conductive member is formed inside the opening to be connected with the electric wiring, the conductive member may be used as an external connection terminal for connecting the conductive member with an external device, so that it can be used for a wiring board of a semiconductor device of LGA type. In this case, when a thickness of the conductive member is made to be thinner than that of the insulating substrate, projection of an external connection terminal to be connected with an external device from the insulating substrate can be prevented, and the resulting wiring board can be thinned. In this case, however, when the conductive member is too thin, there is a possibility of occurring poor connection, because a soldering paste or the like used in case of connecting the conductive member with an external device is not sufficiently soaked up into the opening. For this reason, it is preferred that a thickness of the conductive member is equal to xc2xd or more than that of the insulating substrate.
Furthermore, when a thickness of the conductive member is made to be thinner than that of the insulating substrate, it results easily in a cause for poor connection due to remaining air inside the opening in the case when a soldering paste or the like is soaked up into the opening. For this reason, when a concave conductive member having a thinner thickness at the central portion of the opening than that of a vicinity of a side wall of the opening is prepared, air in the opening makes easily away along a curved surface towards the outside, resulting in reduction of occurrence of voids due to remaining air in the opening.
Moreover, the conductive member may be made from copper (Cu), nickel (Ni), silver (Ag) or the like. In this case, it is preferred that a nickel (Ni) thin film layer and a gold (Au) thin film layer are disposed on a surface of the conductive member in order to achieve good bond properties with respect to a solder.
(2) A semiconductor device according to the present invention wherein a wiring board in which an opening is defined at a predetermined position of a film-like insulating substrate, an electric wiring provided with a connection terminal covering the opening is disposed on a principal plane of the insulating substrate, and a conductive member to be connected with the connection terminal of the electric wiring is disposed inside the opening is placed; a semiconductor chip is placed on the surface of the wiring board on which the electric wiring has been disposed; the electric wiring of the wiring board is electrically connected with an external electrode of the semiconductor chip; and the semiconductor chip, the electric wiring, and connecting section for the electric wiring and the external electrode of the semiconductor chip are sealed with a sealing insulator, comprises the conductive member having a thickness from a surface on which the electric wiring of the insulating substrate has been formed being thinner than that of the insulating substrate.
According to the present invention described in the above paragraph (2), when the wiring board described in the above paragraph (1) is employed, such a semiconductor device of LGA type wherein a conductive member disposed in an opening of the insulating substrate is utilized as a connection terminal for an external device can be obtained. Accordingly, there is no case where such a connection terminal for an external device protrudes from the wiring board as in a conventional semiconductor device of BAG type, so that a resulting semiconductor device can be thinned.
The semiconductor device described in the above paragraph (2) may be the one of face up mounting type wherein the semiconductor chip is placed in such that a surface opposed to the surface on which the external electrode has been formed is opposed to the wiring board, and the external electrode is connected with an electric wiring by means of a bonding wire. Further, the semi conductor device of the above paragraph (2) may be the one of faced own mounting (flip-chip mounting) type wherein the semiconductor chip is placed in such that the external electrode is disposed so as to oppose to the wiring board, and the external electrode is connected with an electric wiring by means of a protrusion conductor.
It is preferred that a thickness of the above-described conductive member is equal to or thinner than that of the above-described insulating substrate so as not to protrude from the insulating substrate. However, when a thickness of the conductive member is too thin, there arises a cause of poor connection in case of connecting an external device. For this reason, it is preferred that a thickness of the conductive member is xc2xd or more of that of the insulating substrate.
On one hand, in the case where a thickness of the conductive member is made thinner than that of the insulating substrate, for example, a soldering paste, which has been applied to a connection terminal section of an external device, is soaked up in the opening to be connected with the conductive member. In this case, when a surface of the conductive member is flat, air remains in the opening to generate voids, and it results easily in a cause for poor connection. For this reason, when a concave conductive member having a thinner thickness at the central portion of the opening than that of a vicinity of a sidewall of the opening is disposed, air in the opening makes easily away outside the opening along the curved surface of the conductive member, whereby poor connection due to voids can be reduced.
Moreover, it is preferred that a conductive member be made from any member selected from the group consisting of copper (Cu), nickel (Ni), and silver (Ag). It is also preferred that a thin film layer made of nickel (Ni) and a thin film layer made of gold (Au) are placed on a surface of the conductive member in order to improve bonding properties with respect to a soldering paste.
(3) A process for the production of a wiring board according to the present invention comprises the steps of defining an opening at a predetermined position of a film-like insulating substrate; forming a conductive thin film on a principal plane of the insulating substrate; etching the conductive thin film to form an electric wiring provided with a connection terminal covering the opening; and forming a conductive member having a thickness equal to or thinner than that of the insulating substrate.
According to the process of the invention described in the above paragraph (3), which is to be applied for a production of a wiring board used in a semiconductor device of LGA type, an opening is defined at a predetermined position of the insulating substrate, in other words, a position at which an external connection terminal for connecting an external device is to be formed, a conductive member is formed inside the opening, and the conductive member is used as an external connection terminal, whereby a wiring board used for a semiconductor device of LGA type can be produced by the use of a single-sided wiring tape material wherein a conductive thin film has been formed on a principal plane (either side) of the insulating substrate. For this reason, steps for producing a wiring board used for a semiconductor device of LGA type become simple, besides its material cost can be reduced, so that cost of manufacture for the wiring board can be reduced.
Furthermore, in the process for the production of a wiring board described in the above paragraph (3), when a thin film layer made of nickel (Ni) and a thin film layer made of gold (Au) are sequentially disposed on surfaces of the electric wiring and the conductive member after forming the conductive member, connection reliability of the conductive member and the external device can be improved.
Moreover, in the process for the production of a wiring board described in the above paragraph (3), a step for forming the conductive member may be effected by forming a copper (Cu) plating or a nickel (Ni) plating in accordance with electroplating method, whereby the conductive member can be easily produced. Further, the above-described step for forming the conductive member may be effected by forming a nickel (Ni) plating in accordance with electroless plating method. In addition, a step other than that described above, for example, the one for forming the conductive member maybe effected by such a manner that the inside of the opening is filled with a conductive paste of silver (Ag) or copper (Cu) and the conductive paste is solidified.
Besides, the above-described step for forming the conductive member may be effected by such a manner that a concave conductive member has a thinner thickness at the central portion of the opening than that of a vicinity of a side wall of the opening, whereby connection reliability of the conductive member and a connection terminal of an external device can be elevated. In this case, when the above-described conductive member is formed in accordance with, for example, a plating method, an amount of a leveler to be added to a plating solution for improving evenness of the conductive member (plating layer) is adjusted, so that a concave plating layer can be formed.